Silicon Carbide Tritium Permeation Barriers for Steel Structural Components

The reactor design proposed by the United States for the International Thermonuclear Experimental Reactor (ITER) requires development of advanced materials for breeder blankets. Aluminized coatings developed over the last several years for tritium permeation barriers work well in the laboratory but fail in radiation environments. Because silicon carbide (SiC) applied via chemical vapor deposition (CVD) does not lose tritium permeability resistance under radiation, this project will develop a material system that uses fully dense CVD SiC as a tritium barrier bonded to ferritic steel, with a SiC foam or a ductile metallic foam layer serving as a compliant interlayer between the steel and the CVD SiC tritium barrier. The composite structure offers significant advantages over current aluminized coatings, including high resistance to thermal- and radiation-induced stress, lower tritium diffusivity and solubility, and compatibility with the molten lead-lithium breeder/coolant. In Phase I, the initial bonding of SiC foam/SiC-tritium-barrier specimens to ferritic steel substrates was demonstrated. A matrix of dense SiC wafers was fabricated for deuterium permeation and tritium plasma testing. Resistance to high temperature thermal cycling and thermal shock was demonstrated through furnace testing, and barrier component bond strength was established through shear testing. The test results indicated that the concept has high potential for meeting the tritium barrier requirements of ITER test blanket modules. In Phase II, the material system will be used in the fabrication of a tritium-barrier tube liner, and performance will be demonstrated by subjecting the component to deuterium permeation and deuterium/tritium plasma experiments. Commercial Applications and Other Benefits as described by the awardee: Nuclear fusion is an ideal alternative to increasingly scarce and expensive fossil fuels and can provide a much greater quantity of environmentally sound energy than wind, solar, and geothermal sources. Practical application of fusion for efficient electricity generation requires the development of materials and structures that can withstand the demanding reactor environment. The proposed barrier material would be a key safety component within reactors that ultimately would be scaled up for commercial use.